1. Field of the Invention
The present invention relates to a method for fabricating a nano-sized diamond whisker, and in particular a nano-sized diamond whisker which can be applied to a highly efficient cold cathode device and to a composite material, by fabricating a surface of diamond or a whole diamond, the diamond which is formed in a film or a particle, in a nano-sized whisker by a plasma etching process.
2. Description of the Background Art
In general, diamond has the following mechanical properties; the highest hardness, the highest thermal conductivity among existing materials, a low thermal expansion coefficient, a superior electrical resistance, a chemical resistance property, a radiation resistance property, an excellent semi-conductivity, and a superior negative electron affinity, and thus the application scope thereof is considerably wide. Especially, the development of a composite material using the thermal and mechanical properties of diamond is very significant in a composite material requiring good mechanical properties (Materials for electronic packaging, D. D. L. Chung, part III, Butterworth-Heinemann, USA(1995)).
However, in order to fabricate a diamond composite material, the diamond must be fabricated in a whisker or a fiber form. The current technology can only fabricate diamonds in the form of a film or a powder (Synthetic Diamond, ed. by K. E. Spear and J. P. Dismukes, John Wiley and Sons, Inc., N.Y., USA(1994)).
When a diamond is fabricated in a whisker or fiber form, the main application is a cold cathode for a field emission device. The cold cathode for the field emission device serves to emit electrons in a field emission flat display panel, a vacuum semiconductor device, a microwave device and the like. Diamond has been recognized as an ideal material for cold cathode due to its negative electron affinity. However, it is difficult to fabricate a diamond in a proper shape, and thus it is not practically useful. If a diamond can be fabricated in a whisker form which can focus an electric field to a cathode portion, it is possible to fabricate a device with remarkably superior field emission performance and durability, as compared with a Spindt-shaped Si or Mo cold cathode (C. A. Spindt, J. Appl. Phys., 39, 3504(1968)) which is being currently used, or a carbon nano-tube (Z. F. Ren et al., Science, 282, 6, November, 110(1998)) which is currently noteworthy.
As disclosed in U.S. Pat. No. 4,957,591, there is a technique of fabricating a diamond crystal particle in a polygonal cone shape. According to this method, polygonal cone-shaped diamond particles are separated by selectively etching a grain boundary between crystals of a polycrystalline diamond film having a polygonal cone-shaped structure by a chemical reaction. The diameter of the polygonal cone-shaped diamond to be fabricated after the etching process is dependent upon the size of the particles composing the diamond film. As the diameter of the polygonal cone-shaped diamond particles composing the diamond film is over a few xcexcm, the diameter of the diamond fabricated by the selective etching process is over 1 to 2 xcexcm. In addition, the diameter of the polygonal cone-shaped diamond increases from narrow to wide, and thus it is impossible to fabricate a bar-shaped diamond having a constant diameter. This technique employs the selective etching process of the grain boundaries of the diamond film, and thus the possibility of fabrication is determined by the microstructure of the diamond film used. When the diamond film is synthesized, its microstructure must be precisely controlled. As a result, the bar-shaped diamond having a diameter equal to or less than 1 xcexcm cannot be fabricated by the above-described method. The etching pressure is considerably high, about 1 to 200 torr, and thus a large sized diamond cannot be regularly etched. The deposition temperature is also high, about 400 to 1000xc2x0 C., and thus only a specific kind of substrate can be employed for deposition of the diamond film, and the diamond may be transformed into graphite. Since the bar-shaped diamond having a constant diameter cannot be fabricated, an application scope thereof is also limited. Further, even if the grain boundaries of the polycrystalline diamond film are selectively etched, it is impossible to fabricate a nano-sized diamond whisker having a constant diameter.
As described above, there is no known method for fabricating a diamond whisker having a constant nano-sized diameter, and thus a technique of fabricating a product utilizing a nano-sized diamond whisker has never been suggested.
Accordingly, it is an object of the present invention to provide a diamond whisker having a constant nano-sized diameter, and to provide a method by which the nano-sized diameter whisker can be fabricated in large area units at a low temperature, by using a real time mask and an anisotropic etching property of diamond.
In order to achieve the above-described objects of the present invention, there is provided a method for fabricating a nano-sized diamond whisker comprising the steps of: depositing a diamond film on a substrate; forming a nano-sized pattern on the deposited diamond film; and etching the diamond film by using the nano-sized pattern as an etching mask. The pattern may be grown and formed on the diamond film in the shape of an island or a Stranski-Krastanov type. In addition, a material reacted with plasma or ions at a reactive chamber wall or a substrate supporting unit may be deposited on the substrate, and then the nano-sized diamond whisker may be fabricated by using the deposited material as a mask. A reactive plasma or reactive ion beam is used in the step of etching the diamond film.